Design an Embeddable Pay by Bank Widget
Company: Plaid
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Onsite
Overview: Design an embeddable Pay by Bank widget that isolates bank authentication inside an iframe and communicates through a validated postMessage channel. Trace browser and backend APIs, secret boundaries, asynchronous payment state, retries, origin validation, observability, and launch tradeoffs.